This invention relates to a frictional damper, especially useful in washing machines with a spinning mode, which has a circular-cylindrical casing and a ram which is coaxially displaceable in the casing and one end of which projects from the casing and the other end of which is provided with an approximately cylindrical friction piston. The invention relates, more particular to such a frictional damper in which the piston is provided on one external face with one or more friction elements which are elastically pressed against the inner wall of the casing.
In a frictional damper of the above-mentioned type, known from British Patent Specification No. 1,523,497, the friction piston consists of at least three elements which are formed from cylinder sections provided on their external face with friction elements. These cylinder sections are provided on their external face with recesses in which friction elements of felt are located. On their inside, the cylinder sections are radially under the load of an annular spring. In the case of wear of the friction elements, this design makes so-called wear readjustment possible. However, because the cylinder sections have an exactly circular outline only if they are arranged on a well-defined circular arc, there is no guarantee that, over the full life of such a frictional damper, the specific surface pressure of the friction elements against the associated inner wall of the casing is or remains equal at all points of the friction elements. This also has the undesirable consequence that the friction characteristics of such a frictional damper vary over its life time.
From the German Federal Repulic Offenlegungsschrift (Laid Open Patent Application) No. 1,950,794, a frictional damper is known, the friction piston of which includes an outer friction element, formed from a strip folded together to give an annular cylinder, and of an inner annular body of an elastically yielding material which is compressibly arranged between two annular discs. The outer friction element is glued onto the inner annular body. To balance wear and to set a desired frictional force, the inner annular body can be pretensioned. This design necessarily results in a cambered shape of the friction piston, that is to say, also in this case, the specific surface pressure between the surface of the friction element and the associated inner wall of the casing is not equal over the entire surface of the friction element.